diff --git a/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp b/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
--- a/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
@@ -78,6 +78,8 @@
   const bool HasFP16 = ST.hasFullFP16();
   const LLT &MinFPScalar = HasFP16 ? s16 : s32;
 
+  const bool HasCSSC = ST.hasCSSC();
+
   getActionDefinitionsBuilder({G_IMPLICIT_DEF, G_FREEZE})
       .legalFor({p0, s8, s16, s32, s64})
       .legalFor(PackedVectorAllTypeList)
@@ -668,7 +670,12 @@
       .lowerIf(isVector(0))
       .clampScalar(0, s32, s64)
       .scalarSameSizeAs(1, 0)
-      .customFor({s32, s64});
+      .legalIf([=](const LegalityQuery &Query) {
+        return (HasCSSC && typeInSet(0, {s32, s64})(Query));
+      })
+      .customIf([=](const LegalityQuery &Query) {
+        return (!HasCSSC && typeInSet(0, {s32, s64})(Query));
+      });
 
   getActionDefinitionsBuilder(G_SHUFFLE_VECTOR)
       .legalIf([=](const LegalityQuery &Query) {
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz-zero-undef.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz-zero-undef.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz-zero-undef.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz-zero-undef.mir
@@ -1,6 +1,6 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple=aarch64 -global-isel -verify-machineinstrs -run-pass=legalizer %s -o - | FileCheck %s
-
+# RUN: llc -mtriple=aarch64 -global-isel -verify-machineinstrs -mattr=+cssc -run-pass=legalizer %s -o - | FileCheck %s --check-prefix=CHECK-CSSC
 ...
 ---
 name:            s8
@@ -10,14 +10,25 @@
     liveins: $w0
     ; CHECK-LABEL: name: s8
     ; CHECK: liveins: $w0
-    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
-    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 256
-    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
-    ; CHECK: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE [[OR]]
-    ; CHECK: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
-    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
-    ; CHECK: $w0 = COPY [[COPY]](s32)
-    ; CHECK: RET_ReallyLR implicit $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 256
+    ; CHECK-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-NEXT: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE [[OR]]
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
+    ; CHECK-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s8
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-CSSC-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 256
+    ; CHECK-CSSC-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ [[OR]](s32)
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s8) = G_IMPLICIT_DEF
     %cttz:_(s8) = G_CTTZ_ZERO_UNDEF %val(s8)
     %ext:_(s32) = G_ANYEXT %cttz(s8)
@@ -33,14 +44,25 @@
     liveins: $w0
     ; CHECK-LABEL: name: s16
     ; CHECK: liveins: $w0
-    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
-    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65536
-    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
-    ; CHECK: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE [[OR]]
-    ; CHECK: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
-    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
-    ; CHECK: $w0 = COPY [[COPY]](s32)
-    ; CHECK: RET_ReallyLR implicit $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65536
+    ; CHECK-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-NEXT: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE [[OR]]
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
+    ; CHECK-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s16
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-CSSC-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65536
+    ; CHECK-CSSC-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ [[OR]](s32)
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s16) = G_IMPLICIT_DEF
     %cttz:_(s16) = G_CTTZ_ZERO_UNDEF %val(s16)
     %ext:_(s32) = G_ANYEXT %cttz(s16)
@@ -58,11 +80,19 @@
 
     ; CHECK-LABEL: name: s32
     ; CHECK: liveins: $w0
-    ; CHECK: %val:_(s32) = COPY $w0
-    ; CHECK: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE %val
-    ; CHECK: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
-    ; CHECK: $w0 = COPY [[CTLZ]](s32)
-    ; CHECK: RET_ReallyLR implicit $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %val:_(s32) = COPY $w0
+    ; CHECK-NEXT: [[BITREVERSE:%[0-9]+]]:_(s32) = G_BITREVERSE %val
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
+    ; CHECK-NEXT: $w0 = COPY [[CTLZ]](s32)
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s32
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: %val:_(s32) = COPY $w0
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ %val(s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s32) = COPY $w0
     %1:_(s32) = G_CTTZ_ZERO_UNDEF %val(s32)
     $w0 = COPY %1(s32)
@@ -79,11 +109,19 @@
 
     ; CHECK-LABEL: name: s64
     ; CHECK: liveins: $x0
-    ; CHECK: %val:_(s64) = COPY $x0
-    ; CHECK: [[BITREVERSE:%[0-9]+]]:_(s64) = G_BITREVERSE %val
-    ; CHECK: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[BITREVERSE]](s64)
-    ; CHECK: $x0 = COPY [[CTLZ]](s64)
-    ; CHECK: RET_ReallyLR implicit $x0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %val:_(s64) = COPY $x0
+    ; CHECK-NEXT: [[BITREVERSE:%[0-9]+]]:_(s64) = G_BITREVERSE %val
+    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[BITREVERSE]](s64)
+    ; CHECK-NEXT: $x0 = COPY [[CTLZ]](s64)
+    ; CHECK-NEXT: RET_ReallyLR implicit $x0
+    ; CHECK-CSSC-LABEL: name: s64
+    ; CHECK-CSSC: liveins: $x0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: %val:_(s64) = COPY $x0
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s64) = G_CTTZ %val(s64)
+    ; CHECK-CSSC-NEXT: $x0 = COPY [[CTTZ]](s64)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $x0
     %val:_(s64) = COPY $x0
     %1:_(s64) = G_CTTZ_ZERO_UNDEF %val(s64)
     $x0 = COPY %1(s64)
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz.mir
@@ -1,5 +1,6 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple=aarch64 -global-isel -verify-machineinstrs -run-pass=legalizer %s -o - | FileCheck %s
+# RUN: llc -mtriple=aarch64 -global-isel -verify-machineinstrs -mattr=+cssc -run-pass=legalizer %s -o - | FileCheck %s --check-prefix=CHECK-CSSC
 
 ...
 ---
@@ -19,6 +20,16 @@
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
     ; CHECK-NEXT: $w0 = COPY [[COPY]](s32)
     ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s8
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-CSSC-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 256
+    ; CHECK-CSSC-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ [[OR]](s32)
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s8) = G_IMPLICIT_DEF
     %cttz:_(s8) = G_CTTZ %val(s8)
     %ext:_(s32) = G_ANYEXT %cttz(s8)
@@ -43,6 +54,16 @@
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
     ; CHECK-NEXT: $w0 = COPY [[COPY]](s32)
     ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s16
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-CSSC-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65536
+    ; CHECK-CSSC-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[DEF]], [[C]]
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ [[OR]](s32)
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[COPY]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s16) = G_IMPLICIT_DEF
     %cttz:_(s16) = G_CTTZ %val(s16)
     %ext:_(s32) = G_ANYEXT %cttz(s16)
@@ -66,6 +87,13 @@
     ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[BITREVERSE]](s32)
     ; CHECK-NEXT: $w0 = COPY [[CTLZ]](s32)
     ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s32
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: %val:_(s32) = COPY $w0
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s32) = G_CTTZ %val(s32)
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[CTTZ]](s32)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
     %val:_(s32) = COPY $w0
     %1:_(s32) = G_CTTZ %val(s32)
     $w0 = COPY %1(s32)
@@ -88,6 +116,13 @@
     ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[BITREVERSE]](s64)
     ; CHECK-NEXT: $x0 = COPY [[CTLZ]](s64)
     ; CHECK-NEXT: RET_ReallyLR implicit $x0
+    ; CHECK-CSSC-LABEL: name: s64
+    ; CHECK-CSSC: liveins: $x0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: %val:_(s64) = COPY $x0
+    ; CHECK-CSSC-NEXT: [[CTTZ:%[0-9]+]]:_(s64) = G_CTTZ %val(s64)
+    ; CHECK-CSSC-NEXT: $x0 = COPY [[CTTZ]](s64)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $x0
     %val:_(s64) = COPY $x0
     %1:_(s64) = G_CTTZ %val(s64)
     $x0 = COPY %1(s64)
@@ -113,8 +148,21 @@
     ; CHECK-NEXT: [[CTPOP:%[0-9]+]]:_(<4 x s32>) = G_CTPOP [[AND]](<4 x s32>)
     ; CHECK-NEXT: $q0 = COPY [[CTPOP]](<4 x s32>)
     ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    ; CHECK-CSSC-LABEL: name: v4s32
+    ; CHECK-CSSC: liveins: $q0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: %val:_(<4 x s32>) = COPY $q0
+    ; CHECK-CSSC-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 -1
+    ; CHECK-CSSC-NEXT: [[BUILD_VECTOR:%[0-9]+]]:_(<4 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32), [[C]](s32), [[C]](s32)
+    ; CHECK-CSSC-NEXT: [[XOR:%[0-9]+]]:_(<4 x s32>) = G_XOR %val, [[BUILD_VECTOR]]
+    ; CHECK-CSSC-NEXT: [[ADD:%[0-9]+]]:_(<4 x s32>) = G_ADD %val, [[BUILD_VECTOR]]
+    ; CHECK-CSSC-NEXT: [[AND:%[0-9]+]]:_(<4 x s32>) = G_AND [[XOR]], [[ADD]]
+    ; CHECK-CSSC-NEXT: [[CTPOP:%[0-9]+]]:_(<4 x s32>) = G_CTPOP [[AND]](<4 x s32>)
+    ; CHECK-CSSC-NEXT: $q0 = COPY [[CTPOP]](<4 x s32>)
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $q0
     %val:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = G_CTTZ %val(<4 x s32>)
     $q0 = COPY %1(<4 x s32>)
     RET_ReallyLR implicit $q0
+
 ...
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/select-cttz.mir b/llvm/test/CodeGen/AArch64/GlobalISel/select-cttz.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/select-cttz.mir
@@ -0,0 +1,64 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -O0 -mtriple=arm64-unknown-unknown -global-isel -run-pass=instruction-select -global-isel-abort=1 %s -o - | FileCheck %s
+# RUN: llc -O0 -mtriple=arm64-unknown-unknown -global-isel -mattr=+cssc -run-pass=instruction-select -global-isel-abort=1 %s -o - | FileCheck %s --check-prefix=CHECK-CSSC
+...
+---
+name:            s32
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $w0
+    ; CHECK-LABEL: name: s32
+    ; CHECK: liveins: $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr32 = COPY $w0
+    ; CHECK-NEXT: [[RBITWr:%[0-9]+]]:gpr32 = RBITWr [[COPY]]
+    ; CHECK-NEXT: [[CLZWr:%[0-9]+]]:gpr32 = CLZWr [[RBITWr]]
+    ; CHECK-NEXT: $w0 = COPY [[CLZWr]]
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    ; CHECK-CSSC-LABEL: name: s32
+    ; CHECK-CSSC: liveins: $w0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:gpr32 = COPY $w0
+    ; CHECK-CSSC-NEXT: [[CTZWr:%[0-9]+]]:gpr32 = CTZWr [[COPY]]
+    ; CHECK-CSSC-NEXT: $w0 = COPY [[CTZWr]]
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $w0
+    %0:gpr(s32) = COPY $w0
+    %1:gpr(s32) = G_CTTZ %0(s32)
+    $w0 = COPY %1(s32)
+    RET_ReallyLR implicit $w0
+
+...
+---
+name:            s64
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0
+    ; CHECK-LABEL: name: s64
+    ; CHECK: liveins: $x0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x0
+    ; CHECK-NEXT: [[RBITXr:%[0-9]+]]:gpr64 = RBITXr [[COPY]]
+    ; CHECK-NEXT: [[CLZXr:%[0-9]+]]:gpr64 = CLZXr [[RBITXr]]
+    ; CHECK-NEXT: $x0 = COPY [[CLZXr]]
+    ; CHECK-NEXT: RET_ReallyLR implicit $x0
+    ; CHECK-CSSC-LABEL: name: s64
+    ; CHECK-CSSC: liveins: $x0
+    ; CHECK-CSSC-NEXT: {{  $}}
+    ; CHECK-CSSC-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x0
+    ; CHECK-CSSC-NEXT: [[CTZXr:%[0-9]+]]:gpr64 = CTZXr [[COPY]]
+    ; CHECK-CSSC-NEXT: $x0 = COPY [[CTZXr]]
+    ; CHECK-CSSC-NEXT: RET_ReallyLR implicit $x0
+    %0:gpr(s64) = COPY $x0
+    %1:gpr(s64) = G_CTTZ %0(s64)
+    $x0 = COPY %1(s64)
+    RET_ReallyLR implicit $x0
+
+...